What would happened if I called 911 in this situation? Do I have any other options?

Simply put, my brother's threatened violence against me multiple times, and his mentality seems unstable enough to me that he would do it. He's recently stepped it up to threats against my life, and since he had physically harmed me during several encounters before, I'm not going to try to doubt him. Mental help is not an option in this situation. No one in my family knows what to do, but he's really scaring me. We've tried talking and reasoning with him on many occasions over the years, but his issues run deeper than whatever triggers his tantrums, and he always focuses them on me. We've decided that if I'm home alone with him and the situation turns serious, I have the option to dial 911. What would happen to him if I did this? Do I have any other options, besides mental help or reasoning?